Tropical Storm Francine Discussion Number 4
NWS National Hurricane Center Miami FL AL062024
1000 AM CDT Mon Sep 09 2024
The structure of the system on satellite imagery has improved this
morning, with a large circular region of cold convection between -70
to -85 near the estimated center. An Air-Force Reconnaissance
Aircraft is sampling the system this morning and earlier found a
cyclonic wind shift from southeasterly to northwesterly flow near
the center of the mass of deep convection. This data provides enough
evidence that a well-defined circulation now exists, and thus PTC
Six has become Tropical Storm Francine with sustained winds of
45 kt this advisory.
The estimated motion is still tricky given the center only recently
formed but is estimated still off to the north-northwest at 340/4
kt. The system is expected to gradually turn northward and then
north-northeastward as it moves between a mid-level ridge centered
over Cuba and a broad mid- to upper-level trough located to its
northwest over Texas. The guidance this cycle has shifted a little
eastward and faster, and the NHC track forecast was once again
nudged in that direction. The current track splits the difference
between HCCA and TVCN and still shows Francine moving ashore of
Louisiana sometime on Wednesday evening. There remains a decent
amount of track uncertainty with the GEFS and EPS ensembles showing
along-track spread implying some speed differences near landfall.
While the system is now a tropical storm, the inner core wind field
per reconnaissance observations is still broad and in the organizing
stage, and initial intensification will be gradual. However, after
an inner-core becomes established, and assuming the cyclone's
vertical structure becomes aligned, a period of more significant
intensification is possible while storm is embedded in a low shear,
high mid-level moisture, and over very warm 30-31 C sea-surface
temperatures. The SHIPS rapid intensification (RI) indices are
pretty elevated, and a period of RI could also occur between 24-48
h. For now, the NHC intensity forecast will not explicitly forecast
RI, but is higher than the previous cycle and shows a 75 kt peak in
48 h, in good agreement with the intensity consensus aids. After
that period, southwesterly vertical wind shear quickly increases
from 10 kt to more than 30 kt and the intensity could plateau as it
approaches the northwestern U.S. Gulf coastline, though the system
is forecast to remain a hurricane at landfall. The NHC intensity
forecast continues to be in good agreement with the consensus aids,
but is a bit under the HAFS-A/B and COAMPS-TC models.
FORECAST POSITIONS AND MAX WINDS
INIT 09/1500Z 23.0N 94.9W 45 KT 50 MPH
12H 10/0000Z 24.0N 95.4W 50 KT 60 MPH
24H 10/1200Z 24.9N 95.7W 55 KT 65 MPH
36H 11/0000Z 26.3N 95.0W 65 KT 75 MPH
48H 11/1200Z 28.0N 93.5W 75 KT 85 MPH
60H 12/0000Z 29.7N 92.2W 75 KT 85 MPH...ON THE COAST
72H 12/1200Z 32.4N 90.7W 35 KT 40 MPH...INLAND
96H 13/1200Z 36.2N 89.6W 25 KT 30 MPH...POST-TROPICAL
120H 14/1200Z 37.5N 88.8W 20 KT 25 MPH...POST-TROPICAL
$$
Forecaster Papin
NWS National Hurricane Center Miami FL AL062024
1000 AM CDT Mon Sep 09 2024
The structure of the system on satellite imagery has improved this
morning, with a large circular region of cold convection between -70
to -85 near the estimated center. An Air-Force Reconnaissance
Aircraft is sampling the system this morning and earlier found a
cyclonic wind shift from southeasterly to northwesterly flow near
the center of the mass of deep convection. This data provides enough
evidence that a well-defined circulation now exists, and thus PTC
Six has become Tropical Storm Francine with sustained winds of
45 kt this advisory.
The estimated motion is still tricky given the center only recently
formed but is estimated still off to the north-northwest at 340/4
kt. The system is expected to gradually turn northward and then
north-northeastward as it moves between a mid-level ridge centered
over Cuba and a broad mid- to upper-level trough located to its
northwest over Texas. The guidance this cycle has shifted a little
eastward and faster, and the NHC track forecast was once again
nudged in that direction. The current track splits the difference
between HCCA and TVCN and still shows Francine moving ashore of
Louisiana sometime on Wednesday evening. There remains a decent
amount of track uncertainty with the GEFS and EPS ensembles showing
along-track spread implying some speed differences near landfall.
While the system is now a tropical storm, the inner core wind field
per reconnaissance observations is still broad and in the organizing
stage, and initial intensification will be gradual. However, after
an inner-core becomes established, and assuming the cyclone's
vertical structure becomes aligned, a period of more significant
intensification is possible while storm is embedded in a low shear,
high mid-level moisture, and over very warm 30-31 C sea-surface
temperatures. The SHIPS rapid intensification (RI) indices are
pretty elevated, and a period of RI could also occur between 24-48
h. For now, the NHC intensity forecast will not explicitly forecast
RI, but is higher than the previous cycle and shows a 75 kt peak in
48 h, in good agreement with the intensity consensus aids. After
that period, southwesterly vertical wind shear quickly increases
from 10 kt to more than 30 kt and the intensity could plateau as it
approaches the northwestern U.S. Gulf coastline, though the system
is forecast to remain a hurricane at landfall. The NHC intensity
forecast continues to be in good agreement with the consensus aids,
but is a bit under the HAFS-A/B and COAMPS-TC models.
FORECAST POSITIONS AND MAX WINDS
INIT 09/1500Z 23.0N 94.9W 45 KT 50 MPH
12H 10/0000Z 24.0N 95.4W 50 KT 60 MPH
24H 10/1200Z 24.9N 95.7W 55 KT 65 MPH
36H 11/0000Z 26.3N 95.0W 65 KT 75 MPH
48H 11/1200Z 28.0N 93.5W 75 KT 85 MPH
60H 12/0000Z 29.7N 92.2W 75 KT 85 MPH...ON THE COAST
72H 12/1200Z 32.4N 90.7W 35 KT 40 MPH...INLAND
96H 13/1200Z 36.2N 89.6W 25 KT 30 MPH...POST-TROPICAL
120H 14/1200Z 37.5N 88.8W 20 KT 25 MPH...POST-TROPICAL
$$
Forecaster Papin
